The present invention relates to annular hole cutters and more particularly to annular hole cutters used to cut holes in railroad rails for receipt of a connecting bolt.
In repairing or assembling railroad rails, it is common to drill or cut holes in a pair of rails with a drill bit to interconnect the rails with a steel plate. The plate has mating holes and a fastener, such as a bolt, which is inserted through the plate and rail and connected with a nut. Drilling or cutting holes in railroad rails presents numerous problems. The rails are made of very hard steel that is extremely difficult to cut through. Typically, the drilling or cutting can take a long time, for example two to three minutes with a spade bit, forty to forty-five seconds with an indexable carbide cutter. Also the process of cutting the rails quickly dulls the cutting tool or drill requiring either resharpening or replacing the tool. Resharpening can be difficult since the work on the rails may be at remote locations and replacement can be expensive.
The typical drill that is used to form holes in rails is a spade drill or indexable carbide cutter with carbide inserts. Spade drills are slow and require a lot of horsepower to power the spade drill through the rail. This is due to the spade drill cutting all of the steel to form hole in the rail. The power source commonly used with spade drills is a very large gas powered drill motor. These gas powered drill motors are not portable and must be mounted upon a vehicle of some sort to move them along the rail. The gas powered drills are very costly to purchase and to operate when compared to portable gas powered rail cutters and are cumbersome to operate because of the size of the gas powered drill. Additionally, the time required to drill the hole is a problem. Because all the steel is being removed from the rail to form the hole, more time is needed to complete each hole. These drills will typically become dull after one to ten holes have been cut. Users of these spade drills will typically dispose of them and use another new spade drill. An advantage to spade drills is that they are less expensive than known annular hole cutters with carbide inserts. The cost of a spade drill is typically about $7 to $10 and an indexable carbide cutter will cost about $150 and $7 to $10 for the carbide inserts. With these, when the inserts are dulled, they are replaced with new inserts.
Annular hole cutters with brazed carbide inserts are capable of cutting holes in rails more quickly than spade drills and require much less power. Annular hole cutters have a cutter body of a generally inverted cup shape and a shank for attaching the cutter to a drill motor. The end of the cutter body has cutting teeth spaced about it that cut a groove or kerf into the rail. The only steel that is being removed is the steel from the kerf which is being cut by the spaced cutter teeth. When the cut is completely through the rail, a cylindrical slug is left that is ejected from the cavity of the cutter body. The assignee of the present invention has invented numerous annular hole cutters including for example U.S. Pat. No. 4,813,819 and is the owner through assignment of other annular hole cutters.
Because of the minimum amount of steel removed by the annular cutter, lower horsepower is required to power the cutter through the rail. For example, for a typical rail drill, only one horsepower is needed, whereas in spade drills five to ten horsepower is required. Because of the lower horsepower requirements, portable rail drills can be used to power the cutters. An example of a portable rail drill is disclosed in U.S. Pat. No. 5,203,650, which is assigned to the assignee of the present invention. These portable rail drills are much easier to handle than the larger gas powered drills, are less expensive to purchase and less expensive to maintain.
The problem with annular cutters is their cost and the difficulty in resharpening them. They require carbide inserts in order to effectively cut through the hard steel of the rail. Unlike a spade drill which has a pair of cutting edges, annular cutters have a number of teeth, usually 4 to 6 teeth and each requires an insert. This increases their cost and increases the difficulty in resharpening them. It is difficult to have the proper equipment to resharpen these inserts in remote locations. They must be stored and brought to a resharpening center to be resharpened. A task that is not popular among rail workers. Due to their expense, they are not readily disposable either.